Conventionally, a technique for organizing a convoy travel of vehicles, or a platoon travel of vehicles, is known. The convoy travel of vehicle may include a lead vehicle and following vehicles, where a technique for organizing the convoy may control the travel of the following vehicles based on exchange of information through vehicle-to-vehicle wireless communication between terminals on the respective vehicles, for keeping a certain inter-vehicle distance interposed between vehicles. For example, Japanese Patent Laid-Open No. 2000-348300 (JP '300) discloses a convoy travel technique where each of the vehicles in the convoy transmits various information such as the subject vehicle position, amount of operations (e.g., operation amounts of a steering wheel, an accelerator, a brake and the like) and physical quantity (i.e., a vehicle speed, an acceleration, a yaw rate) to the following vehicles at regular intervals, and the following vehicles follow the respective lead vehicles according to received information.
In such convoy travel of the vehicles, the inter-vehicle distance between the vehicles may be reduced to accommodate more vehicles in one convoy, or may be reduced to increase the energy efficiency by the reduction of the travel resistance for each vehicle.
However, conventionally, it is difficult to reduce the inter-vehicle distance in the convoy travel of the vehicles, thereby making it difficult to achieve the advantageous effects of the convoy travel.
More specifically, since the brake capacity and the vehicle weight are different vehicle to vehicle, speed control capacity such as (i) a response time from a start of the braking to a start of speed reduction, (ii) deceleration magnitude designated as maximum deceleration and the like may be different for respective vehicle types. Further, whether the vehicle is equipped with an independent range sensor, which independently detects an inter-vehicle distance to a lead vehicle and whether the range sensor has detected an obstacle or not are closely related to and are substantially affecting the speed control capacity such as a “distance-based” response time or the like, which is detected as a response time for reducing the vehicle speed when a detected inter-vehicle distance is too short to the lead vehicle.
When a vehicle has a lower speed control capacity, such vehicle must have a longer inter-vehicle distance to the lead vehicle, because such vehicle takes a longer time to reduce its speed to a target value. Conventionally, for accommodating the lower speed control capacity vehicles, the convoy travel of the vehicles, used, for all the vehicles in the convoy, a target inter-vehicle distance of the lowest capacity vehicle. Therefore, depending on the vehicles, such target inter-vehicle distance is too long, and the advantages of the convoy travel of the vehicles were destroyed.